Field of the Invention
The illustrative embodiments of the invention relate generally to a pump for fluid and, more specifically, to a pump in which each pumping cavity is substantially a disc-shaped, cylindrical cavity having substantially circular end walls and a side wall and which operates via acoustic resonance of fluid within the cavity. More specifically again, the illustrative embodiments of the invention relate to a pump in which the pump actuator embodies an advanced construction bringing substantial benefit to the pump in its construction, integration into products, and operation.
Description of Related Art
It is known to use acoustic resonance to achieve fluid pumping from defined inlets and outlets. This can be achieved using a long cylindrical cavity with an acoustic driver at one end, which drives a longitudinal acoustic standing wave. In such a cylindrical cavity, the acoustic pressure wave has limited amplitude. Varying cross-section cavities, such as cone, horn-cone, bulb have been used to achieve higher amplitude pressure oscillations thereby significantly increasing the pumping effect. In such higher amplitude waves non-linear mechanisms which result in energy dissipation are suppressed by careful cavity design. However, high amplitude acoustic resonance has not been employed within disc-shaped cavities in which radial pressure oscillations are excited until recently. International Patent Application No. PCT/GB2006/001487, published as WO 2006/111775 (the '487 Application), discloses a pump having a substantially disc-shaped cavity with a high aspect ratio, i.e., the ratio of the radius of the cavity to the height of the cavity.
The pump described in the '487 application is further developed in related patent applications PCT/GB2009/050245, PCT/GB2009/050613, PCT/GB2009/050614, PCT/GB2009/050615, PCT/GB2011/050141. These applications and the '487 Application are included herein by reference.
It is important to note that the pump described in the '487 application and the related applications listed above operates on a different physical principle to the majority of pumps described in the prior art. In particular many pumps known in the art are displacement pumps, i.e. pumps in which the volume of the pumping chamber is made smaller in order to compress and expel fluids therefrom through an outlet valve and is increased in size so as to draw fluid therein through an inlet valve. An example of such a pump is described in DE4422743 (“Gerlach”), and further examples of displacement pumps may be found in US2004000843, WO2005001287, DE19539020, and U.S. Pat. No. 6,203,291.
By contrast, the '487 application describes a pump which operates on the principle of acoustic resonance. In such a pump there exist, in operation, pressure oscillations within the pump cavity such that the fluid is compressed within one part of the cavity while the fluid is simultaneously expanded in another part of the cavity. In contrast to more conventional displacement pump an acoustic resonance a pump does not require a change in the cavity volume in order to achieve pumping operation. Instead, its design is adapted to efficiently create, maintain, and rectify the acoustic pressure oscillations within the cavity.
Turning now to its design and operation in greater detail, the '487 Application describes an acoustic resonance pump which has a substantially cylindrical cavity comprising a side wall closed at each end by end walls, one or more of which is a driven end wall. The pump also comprises an actuator that causes an oscillatory motion of the driven end wall (“displacement oscillations”) in a direction substantially perpendicular to the end wall or substantially parallel to the longitudinal axis of the cylindrical cavity, referred to hereinafter as “axial oscillations” of the driven end wall. The axial oscillations of the driven end wall generate substantially proportional “pressure oscillations” of fluid within the cavity creating a radial pressure distribution approximating that of a Bessel function of the first kind as described in the '487 Application, such oscillations referred to hereinafter as “radial oscillations” of the fluid pressure within the cavity.
Such a pump requires one or more valves for controlling the flow of fluid through the pump and, more specifically, valves being capable of operating at high frequencies, as it is preferable to operate the pump at frequencies beyond the range of human hearing. Such a valve is described in International Patent Application No. PCT/GB2009/050614.
The efficiency of such a pump is dependent upon the interface between the driven end wall and the side wall. It is desirable to maintain the efficiency of such pump by structuring the interface so that it does not decrease or dampen the motion of the driven end wall thereby mitigating any reduction in the amplitude of the fluid pressure oscillations within the cavity. Patent application PCT/GB2009/050613 (the '613 Application) discloses a pump wherein a portion of the driven end wall between the actuator and the side wall provides an interface that reduces damping of the motion of the driven end wall, that portion being referred to therein and hereinafter as an “isolator”. Illustrative embodiments of isolators are shown in the figures of the '613 Application.
More specifically, the pump of the '613 Application comprises a pump body having a substantially cylindrical shape defining a cavity formed by a side wall closed at both ends by substantially circular end walls, at least one of the end walls being a driven end wall having a central portion and a peripheral portion adjacent the side wall, wherein the cavity contains a fluid when in use. The pump further comprises an actuator operatively associated with the central portion of the driven end wall to cause an oscillatory motion of the driven end wall in a direction substantially perpendicular thereto. The pump further comprises an isolator operatively associated with the peripheral portion of the driven end wall to reduce dampening of the displacement oscillations caused by the end wall's connection to the side wall of the cavity. The pump further comprises a first aperture disposed at about the centre of one of the end walls, and a second aperture disposed at any other location in the pump body, whereby the displacement oscillations generate radial oscillations of fluid pressure within the cavity of said pump body causing fluid flow through said apertures.
We now turn to two limiting aspects of the prior art:
Firstly, in operation, the illustrative embodiment of a single-cavity pump shown in FIG. 1A of the '613 Application may generate a net pressure difference across its actuator, putting stress on the bond between the isolator and the pump body and on the bond between the isolator and the actuator component. It is possible that these stresses may lead to failure of one or more of these bonds and it is therefore desirable that they should be strong in order to ensure that the pump delivers a long operational lifetime. Secondly, in order to operate, the single-cavity pump shown in FIG. 1A of the '613 Application requires robust electrical connection to be made to its actuator. This may be achieved by means commonly known in the prior art including by soldered wires or spring contacts which may be conveniently attached the side of the actuator facing away from the pump cavity. However, as disclosed in the '417 Application, a resonant acoustic pump of this kind may also be designed such that two pump cavities are driven by a common driven end wall. Such a two-cavity pump is advantageous as it may deliver increased flow and/or pressure when compared with a single-cavity design, and may deliver increased space, power, or cost efficiency. However in a two-cavity pump it becomes difficult to make electrical contact to the actuator using conventional means without disrupting the acoustic resonance in at least one of the two pump cavities and/or mechanically damping the motion of the actuator. For example, soldered wires or spring contacts may disrupt the acoustic resonance of the cavity in which they are present.
Therefore, for reasons of pump lifetime and performance, a pump construction which achieves a strong bond between the actuator and the isolator, and which facilitates robust electrical connection to the actuator without adversely affecting the resonance of either of the cavities of a two-cavity pump is desirable. The invention described herein describes a combined actuator and isolator assembly which achieves these objectives.